<!DOCTYPE html>
  <html lang="en">
  <head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
      .item{
        height:40px;
        margin:10px 0;
        padding:10px;
        justify-content:center;
        border:1px black solid;
      }
      .flex{
        display:flex;
      }
    </style>
  </head>
  <body>
    <div>
    <div class="item block"></div>
<div class="item block"></div>
<div class="item block"></div>
<div class="flex">
        <div class="item" style="flex:1"></div><div class="item" style="flex:2"></div>
      </div>
<div class="flex">
        <div class="item" style="flex:1"></div><div class="item" style="flex:1"></div><div class="item" style="flex:1"></div>
      </div>
<div class="item block"></div>
<div class="item block"></div>
<div class="item block"></div>
    </div>

  </body>
  </html>